45,652 research outputs found
Decoherence in QED at finite temperature
We consider a wave packet of a charged particle passing through a cavity
filled with photons at temperature T and investigate its localization and
interference properties. It is shown that the wave packet becomes localized and
the interference disappears with an exponential speed after a sufficiently long
path through the cavity.Comment: Latex, 10 page
Identification of nonlinearity in conductivity equation via Dirichlet-to-Neumann map
We prove that the linear term and quadratic nonlinear term entering a
nonlinear elliptic equation of divergence type can be uniquely identified by
the Dirichlet to Neuman map. The unique identifiability is proved using the
complex geometrical optics solutions and singular solutions
A toral diffeomorphism with a non-polygonal rotation set
We construct a diffeomorphism of the two-dimensional torus which is isotopic
to the identity and whose rotation set is not a polygon
Observed decrease in soil and atmosphere temperature coupling in recent decades over northern Eurasia
Coupling of soil-air temperature is fundamentally relevant to various biophysical and biogeochemical functions near the land surface. However, coupling at an interannual scale is less addressed than at finer timescales, such as diurnal and seasonal scales. Here, we show that interannual variability of soil-air temperature coupling decreased significantly during 1984-2013 across 196 stations in northern Eurasia. Coupling at a depth of 0.2 m remained significant in only 53% of stations during 1999-2013, while it was significant in 80% of stations during 1984-1998. Decreased coupling is mainly attributable to air temperature change in the snow-free season and snow cover retreat. Moreover, change in the extreme snow cover frequency also contributes to the decline, while other climate extremes are less influential. The findings can help us to understand long-term land-climate thermal interactions and to evaluate soil temperature profiles simulated by land surface models. Plain Language Summary The near-surface air temperature closely relates to soil temperature, and the strength of this relationship may be altered by the presence of other environmental elements such as snow cover, soil moisture, and vegetation. In this study, by using paired observations at 196 stations collected from 1984 to 2013 over northern Eurasia, we show that coupling of soil-air temperature was not constant and decreased over time. In the European part of the study region, the coupling consistently decreased; however, there was no clear pattern over the permafrost area. We found that this decline may relate to the increase in air temperature during the snow-free season and snow cover retreat over the period. The decreased coupling was also affected by extreme snow cover frequency. Moreover, we found that the decrease in coupling may accelerate if warming continues in the future. Under a changing climate, the compound impacts of multiple environmental changes on the interannual variability of coupling remain uncertain. The results can advance our knowledge of long-term soil-air temperature coupling and help in evaluating soil temperature profiles simulated by land surface models.Peer reviewe
Simplifying Algebra in Feynman Graphs, Part III: Massive Vectors
A T-dualized selfdual inspired formulation of massive vector fields coupled
to arbitrary matter is generated; subsequently its perturbative series modeling
a spontaneously broken gauge theory is analyzed. The new Feynman rules and
external line factors are chirally minimized in the sense that only one type of
spin index occurs in the rules. Several processes are examined in detail and
the cross-sections formulated in this approach. A double line formulation of
the Lorentz algebra for Feynman diagrams is produced in this formalism, similar
to color ordering, which follows from a spin ordering of the Feynman rules. The
new double line formalism leads to further minimization of gauge invariant
scattering in perturbation theory. The dualized electroweak model is also
generated.Comment: 39 pages, LaTeX, 8 figure
Rectification from Radially-Distorted Scales
This paper introduces the first minimal solvers that jointly estimate lens
distortion and affine rectification from repetitions of rigidly transformed
coplanar local features. The proposed solvers incorporate lens distortion into
the camera model and extend accurate rectification to wide-angle images that
contain nearly any type of coplanar repeated content. We demonstrate a
principled approach to generating stable minimal solvers by the Grobner basis
method, which is accomplished by sampling feasible monomial bases to maximize
numerical stability. Synthetic and real-image experiments confirm that the
solvers give accurate rectifications from noisy measurements when used in a
RANSAC-based estimator. The proposed solvers demonstrate superior robustness to
noise compared to the state-of-the-art. The solvers work on scenes without
straight lines and, in general, relax the strong assumptions on scene content
made by the state-of-the-art. Accurate rectifications on imagery that was taken
with narrow focal length to near fish-eye lenses demonstrate the wide
applicability of the proposed method. The method is fully automated, and the
code is publicly available at https://github.com/prittjam/repeats.Comment: pre-prin
Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)
A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin
and coworkers 40 years ago, is revisited to investigate the low-energy, local
vibrations of the A atoms and their influence on the electronic and
superconducting properties of the compound. Polycrystalline samples with A =
Al, Ga, Y, and La are studied through resistivity and heat capacity
measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49,
1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4
K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are
approximately described by the Einstein model with Einstein temperatures of 24
and 8 K, respectively. A weak but significant coupling between the low-energy
modes, which are almost identical to those called rattling in recent study, and
conduction electrons manifests itself as anomalous enhancement in resistivity
at around low temperatures corresponding to the Einstein temperatures.Comment: 12 pages, 5 figures, to be published in J. Phys. Soc. Jp
Inviscid dynamical structures near Couette flow
Consider inviscid fluids in a channel {-1<y<1}. For the Couette flow
v_0=(y,0), the vertical velocity of solutions to the linearized Euler equation
at v_0 decays in time. At the nonlinear level, such inviscid damping has not
been proved. First, we show that in any (vorticity) H^{s}(s<(3/2)) neighborhood
of Couette flow, there exist non-parallel steady flows with arbitrary minimal
horizontal period. This implies that nonlinear inviscid damping is not true in
any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow and for any
horizontal period. Indeed, the long time behavior in such neighborhoods are
very rich, including nontrivial steady flows, stable and unstable manifolds of
nearby unstable shears. Second, in the (vorticity) H^{s}(s>(3/2)) neighborhood
of Couette, we show that there exist no non-parallel steadily travelling flows
v(x-ct,y), and no unstable shears. This suggests that the long time dynamics in
H^{s}(s>(3/2)) neighborhoods of Couette might be much simpler. Such contrasting
dynamics in H^{s} spaces with the critical power s=(3/2) is a truly nonlinear
phenomena, since the linear inviscid damping near Couette is true for any
initial vorticity in L^2
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